Masteries

Offense:
0

Defense:
21

Utility:
9

Why?
Rod of Ages Has health, mana and AP... Check!
Mercury's Treads Has magic resistance and reduces disables hmmmm.... Check!
Soul Shroud Has health, CD reduction and mana regeneration. Yup you guessed it... Check!
Force of Nature Has magic resistance health regeneration with an additional passive health regen to stack with our Happy Hour that's a no brainer.
Frozen Heart Has armor and finishes our hardcap of 40% CD reduction with more mana how can I pass this up?
Rylai's Scepter Giving nice health, ALL our spells a 15% Slow!!! and MORE DAMAGE!!!!

Item Build Example:
Game Start-

x1 Sapphire Crystal
x1 Health Potion
x1 Mana Potion

Early Game-
x1 Catalyst the Protector
x1 Mercury's Treads You can hold off on upgrading this and just get the boots if you want to get RoA faster.
x1 Rod of Ages For increased AP early for farming.

Middle Game-
x1 Rylai's Scepter You want to capitalize on damage early game so you get this before our CD reduction items for increased farming and harassing.
x1 Soul Shroud Next we want to get our CD reduction cap so we can spam that barrel.
x1 Glacial Shroud Note: After this we will be only -5% from hardcap of 40%. If you find your enemy is lacking physical damage you could get a Spirit Visage instead or Banshee's Veil if u have the extra money. but we lose 8% cd reduction and later 13%.

Late Game-
x1 Force of Nature This has amazing synergy with our Strength of Spirit mastery and Passive.
x1 Frozen Heart After this we will finally hit the hard cap of 40% and have decent armor and a handy debuff.